“Any solution will be totally rejected if it does not end Assad’s rule with all of its military and security pillars and if it does not hold accountable all those who took part in the state terrorism,” said the statement, dated Saturday and signed by some of the most formidable Islamist units fighting Assad.

“We consider attending Geneva 2 on any basis other than that mentioned above...treason that requires trials by our courts,” it said, referring to the proposed peace conference.

The declaration was signed by 22 mostly Islamist brigades, including Suqour al-Sham, al-Tawhid and Ahfad al-Rasul, which are seen as backed by Qatar, as well as Ahrar al-Sham Brigade, a major rebel force in eastern Syria, and the smaller al-Sahaba Brigades, which operates around Damascus.

Several officials, including Arab League chief Nabil Elaraby, have said they expect the conference to convene on Nov. 23 in Geneva, though the United States, Russia and the United Nations have all said no date has been officially set.

This week, the Syrian National Coalition resisted calls from Western and Arab countries to commit to attending the peace talks, saying they would not take part if there was any chance that Assad could cling to power.

The coalition is due to meet on Nov. 9 to discuss taking a detailed position on Geneva, according to opposition sources.